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Adsorption of Oxamyl and Dimecron in Montmorillonite Suspensions¹

ABSTRACT

Adsorption of oxamyl and phosphamidon (Dimecron) was determined from dilute solutions of montmorillonite saturated with different cations, e.g., Li⁺, Na⁺, K⁺, Cs⁺, Fe³⁺, and Al³⁺. Adsorption of oxamyl was found to be greater than adsorption of Dimecron. The shapes of the isotherms depended on the exchangeable cations. The adsorption varied directly with the polarizing power of the exchangeable cation and inversely with changes in temperature, organic matter, and ionic strength up to 0.6, after which it became constant. The enthalpy changes (H°) calculated from the temperature coefficient of the equilibrium constant showed that the process is exothermic. The adsorption of pesticides on montmorillonite gives rise to an entropy loss that is higher for trivalent cations. Various studies, e.g., infrared (IR) and x-ray, as well as thermodynamic parameters and Freundlich adsorption isotherms, revealed the existence of protonation or coordination (or both) between exchangeable cations of clay and oxygen of > C=0 group of the pesticides. However, desorption studies showed the presence of physical adsorption.

¹ Contribution from the Department of Chemistry, D.S. College, Aligarh-202001, India.

² Lecturer

Received for publication September 20, 1980. Accepted for publication March 14, 1983.